An official website of the United States government
ABSTRACT Hybridization and interspecific gene flow play a substantial role in the evolution of plant taxa. The eastern North American white oak syngameon, a group of approximately 15 ecologically, morphologically and genomically distinguishable species, has long been recognised as a model system for studying introgressive hybridization in temperate trees. However, the prevalence, genomic context and environmental correlates of introgression in this system remain largely unknown. To assess introgression in the eastern North American white oak syngameon and population structure within the widespreadQuercus macrocarpa, we conducted a rangewide survey ofQ. macrocarpaand four sympatric eastern North American white oak species. Using a Hyb‐Seq approach, we assembled a dataset of 3412 thinned single‐nucleotide polymorphisms (SNPs) in 445 enriched target loci including 62 genes putatively associated with various ecological functions, as well as associated intronic regions and some off‐target intergenic regions (not associated with the exons). Admixture analysis and hybrid class inference demonstrated species coherence despite hybridization and introgressive gene flow (due to backcrossing of F1s to one or both parents). Additionally, we recovered a genetic structure withinQ. macrocarpaassociated with latitude. Generalised linear mixed models (GLMMs) indicate that proximity to range edge predicts interspecific admixture, but rates of genetic differentiation do not appear to vary between putative functional gene classes. Our study suggests that gene flow between eastern North American white oak species may not be as rampant as previously assumed and that hybridization is most strongly predicted by proximity to a species' range margin.
more »
« less
This content will become publicly available on January 27, 2026
Powdery Mildews on North American Oaks: High Levels of Diversity and Pathogen‐Host Coevolution
ABSTRACT Erysiphespecies infecting oaks in North America are common and widespread, but compared to Asia and Europe, the taxonomy and phylogeny of North American species is unknown. The present study addresses this dispairity. Comprehensive multilocus phylogenetic analyses, includingCAM,GAPDH,GS, ITS,RPB2andTUB, revealed a high degree of co‐evolution between North American oaks and theErysiphespp. that infect them. A concatenated multilocus tree and individual trees based on single loci revealed many highly supported species clades. The clades are formally named to conform with the current taxonomic classification. Available names, such asE. abbreviata,E. calocladophoraandE. extensa, are associated with corresponding clades, and are newly circumscribed supported by ex‐type sequences or, if not available, by the designation of epitypes with ex‐epitype sequences.Erysiphe densissimais reintroduced for a clade that corresponds to the old name ‘E. extensavar.curta’. Eight new species are described, includingErysiphe carolinensis,E. gambelii,E. occidentalis,E. phellos,E. pseudoextensa,E. quercophila,E. quercus‐laurifoliaeandE. schweinitziana. A new diagnostically and taxonomically relevant trait associated with the anamorphs of North AmericanErysiphespecies on oaks has been assssed. This is a special conidiophore‐like lateral outgrowth of the superficial hyphae, comparable to ‘aerial hyphae,’ which are also known for species of the powdery mildew genusCystothecawhich also infectQuercusspecies.
more »
« less
- Award ID(s):
- 2402193
- PAR ID:
- 10568628
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Forest Pathology
- Volume:
- 55
- Issue:
- 1
- ISSN:
- 1437-4781
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
ABSTRACT Many coastal marine species experienced Pleistocene gene flow between the North Pacific and Atlantic. Understanding historical connectivity between ocean basins should aid in predicting how regional faunas will respond to recent warming that has intensified trans‐Arctic dispersal. Wetland fauna of the Northwestern Atlantic may have survived in estuarine refugia throughout glacial cycles, or recolonised from the southern coast, North Pacific or Northeastern Atlantic. Here, we used multilocus genetic markers and historical climate data to investigate lineage distribution and connectivity among populations of the nominally cosmopolitan sea slugAlderia modesta, sampled from mudflats on both coasts of the North Pacific and North Atlantic. Mitochondrial DNA clades from European and North American populations were deeply divergent and reciprocally monophyletic; differences at seven polymorphic nuclear loci indicated prolonged absence of trans‐Atlantic gene flow. A Pacific ancestor likely first colonised the Atlantic during the marine biotic interchange of the middle Pliocene ~3.5 Ma. Both mtDNA phylogenetics and nuclear genotype assignments support repeated trans‐Arctic colonisation of the Northwestern Atlantic from the Pacific during inter‐glacial cycles; no gene flow was evident since the last glacial maximum, however. Time‐calibrated coalescent phylogenies, Bayesian skyline plots and haplotype networks all indicated recent population expansions in the Pacific and Europe, but not Northwestern Atlantic. In both the Pacific and Northwestern Atlantic, older lineages persisted in patchy refugia north of glacial margins, while a derived clade of Pacific haplotypes indicates northward post‐LGM expansion. The biogeographical history ofAlderiacontrasts with rocky‐shore taxa that were largely extirpated by glacial advance and recolonised from refugia following the last glacial maximum. Based on molecular differences and distinctions in radular and penial stylet morphology, we resurrect the nameAlderia harvardiensisGould 1870 forAlderiafrom the Northwestern Atlantic and North Pacific;A. modestarefers exclusively to European slugs.more » « less
-
ABSTRACT Shared polymorphisms, loci with identical alleles across species, are of unique interest in evolutionary biology as they may represent cases of selection maintaining ancient genetic variation post‐speciation, or contemporary selection promoting convergent evolution. In this study, we investigate the abundance of shared polymorphism between two members of theDaphnia pulexspecies complex. We test whether the presence of shared mutations is consistent with the action of balancing selection or alternative hypotheses such as hybridization, incomplete lineage sorting or convergent evolution. We analyzed over 2,000 genomes from six taxa in theD. pulexspecies group and examined the prevalence and distribution of shared alleles between the focal species pair, North American and EuropeanD. pulex. We show that North American and EuropeanD. pulexdiverged over 10 million years ago, yet retained tens of thousands of shared polymorphisms. We suggest that the number of shared polymorphisms between North American and EuropeanD. pulexcannot be fully explained by hybridization or incomplete lineage sorting alone. We show that most shared polymorphisms could be the product of convergent evolution, that a limited number appear to be old trans‐specific polymorphisms, and that balancing selection is affecting convergent and ancient mutations alike. Finally, we provide evidence that a blue wavelength opsin gene with trans‐specific polymorphisms has functional effects on behavior and fitness in the wild.more » « less
-
ABSTRACT Humans have a long history of fermenting food and beverages that led to domestication of the baker's yeast,Saccharomyces cerevisiae. Despite their tight companionship with humans, yeast species that are domesticated or pathogenic can also live on trees. Here we used over 300 genomes ofS. cerevisiaefrom oaks and other trees to determine whether tree‐associated populations are genetically distinct from domesticated lineages and estimate the timing of forest lineage divergence. We found populations on trees are highly structured within Europe, Japan, and North America. Approximate estimates of when forest lineages diverged out of Asia and into North America and Europe coincide with the end of the last ice age, the spread of agriculture, and the onset of fermentation by humans. It appears that migration from human‐associated environments to trees is ongoing. Indeed, patterns of ancestry in the genomes of three recent migrants from the trees of North America to Europe could be explained by the human response to the Great French Wine Blight. Our results suggest that human‐assisted migration affects forest populations, albeit rarely. Such migration events may even have shaped the global distribution ofS. cerevisiae. Given the potential for lasting impacts due to yeast migration between human and natural environments, it seems important to understand the evolution of human commensals and pathogens in wild niches.more » « less
-
Abstract Pleistocene diversity was much higher than today, for example there were three distinct wolf morphotypes (dire, gray, Beringian) in North America versus one today (gray). Previous fossil evidence suggested that these three groups overlapped ecologically, but split the landscape geographically. The Natural Trap Cave (NTC) fossil site in Wyoming,USAis an ideally placed late Pleistocene site to study the geographical movement of species from northern to middle North America before, during, and after the last glacial maximum. Until now, it has been unclear what type of wolf was present atNTC. We analyzed morphometrics of three wolf groups (dire, extant North American gray, Alaskan Beringian) to determine which wolves were present atNTCand what this indicates about wolf diversity and migration in Pleistocene North America. Results showNTCwolves group with Alaskan Beringian wolves. This provides the first morphological evidence for Beringian wolves in mid‐continental North America. Their location atNTCand their radiocarbon ages suggest that they followed a temporary channel through the glaciers. Results suggest high levels of competition and diversity in Pleistocene North American wolves. The presence of mid‐continental Beringian morphotypes adds important data for untangling the history of immigration and evolution ofCanisin North America.more » « less
